With the rapid widespread use, mobile terminal apparatuses are used under various environments and by people having a wide variety of demands. For this reason, the mobile terminal apparatuses are required to have higher functions and higher performance than ever. One of them is the improvement of call reception performance during a call. For example, there is a strong demand for a mobile terminal apparatus which can be used without trouble under a noisy environment such as crowds in the street and a construction site, and moreover which can also be comfortably used by hearing-impaired people.
Measures are taken for a conventional mobile terminal apparatus such as increasing sound pressure of a voice coil type dynamic speaker used for a receiver or improving the shape of sound holes for pronouncing. However, there is a limit to the method of transmission through air vibration, and therefore, it is proposed to provide a bone conduction speaker. Telephone sets provided with the bone conduction speaker have a long track record in the field of fixed telephones, and they are also becoming widely available in the field of mobile terminal apparatuses in recent years. An example thereof is shown in FIG. 1.
In FIG. 1, reference numeral 11 is an upper case, 12 is a vibration section arranged on upper case 11, 13 is a lower case, 14 is a hinge, and 15 is a sub liquid crystal display device. Vibration section 12 is designed to produce vibration according to a call reception signal by an excitation section such as a piezoelectric body which is provided inside the mobile terminal apparatus. By making vibration section 12 contact a part of a user's head, for example, cheek bone, it is possible to receive speech uttered by a communicating party by means of bone conduction.
One example of such a mobile terminal apparatus using the bone conduction speaker is proposed in following Patent Document 1.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-348208